That's taking a 10 + bonuses when not under stress. There aren't that many situation not under stress in the EA. Also, level 1 to 4 aren't what I would call experienced.
Failures aren't the result of "I don't have the strength to do that" unless you can never succeed (i.e. DC is higher than 20 + your bonuses). A very strong person can fail to lift a wood plank if they have a cramp for example. 5 minutes later they might be able to do it.
You are right about the level part, I have to do a better job at viewing my party members as noobs for now (even though its hard to do with some of them, because their back stories make them out to be powerful already).
I can see the point with the lifting, however such instances would happen on very rare occasions and you would need some scenario to make it work. For example I could be running a party of characters all high in strength. It's unlikely that everyone would fail. Right now though it does not feel unlikely at all. It feels like I have very close chances to lift that obstacle regardless of what my party composition is.
